1. Field of the Invention
The present invention relates to detonators and, in particular, to non-electric detonators employed for transmitting initiation signals to receptor lines and to explosive charges.
2. Related Art
Detonators are commonly used not only to initiate explosive charges, e.g., booster charges, but also to initiate non-electric, impulse signals in signal lines such as low-energy detonating cords, shock tubes and low velocity signal tubes (“deflagration tubes”) that carry the impulse signal to other devices. Conventional non-electric detonators comprise an output charge of explosive material packed in the closed end of a cylindrical shell, the other end of the shell having an input signal line connected thereto. Conventionally, the shell is crimped onto a bushing surrounding the signal line in the crimp region, to help secure the shell to the line and to close the open end of the shell in order to seal the interior of the shell against the environment. Some detonators include a pyrotechnic or electronic delay element between the output charge and the signal line to interpose a delay between the receipt of the initiation signal in the detonator and the release of the output signal by detonation of the output charge of the detonator. Upon receipt of an initiation signal from the signal line, the detonator is initiated and its output charge generates an explosive output signal that can be used to initiate signals in one or more receptor lines or to detonate an explosive charge. Numerous devices, commonly referred to as “connector blocks”, are known in the art for holding receptor lines in signal-receiving relation to the explosive end of the detonator.
The explosive output charge in a detonator conforms to the interior of the detonator shell in which it is disposed and, inasmuch as the conventional detonator shell has a circular cross section, so too does the output charge. Accordingly, the explosive output charge will have a diameter defined by the interior diameter of the detonator shell. The length of the output charge refers to its depth in the shell. In prior art low-output detonators, the ratio of the length of the explosive charge to its diameter, sometimes below referred to as “the charge L:D ratio”, is typically less than 1, and is commonly about 0.5:1 or less, resulting in a disc-like configuration. For example, a typical prior art detonator will have an outside diameter of about 0.28 to 0.295 inch (about 7.11 to 7.49 mm) and an inside diameter of about 0.26 inch (about 6.60 mm), resulting in the output charge having the same diameter, D, of about 0.26 inch (about 6.60 mm). The typical prior art output charge has a length L (measured along the longitudinal axis of the detonator) of about 0.1 inch (about 2.54 mm), resulting in a charge L:D ratio of about 0.38:1.
As a result of the disc-like configuration of the prior art explosive output charge, the output signal of a prior art detonator is strongest at the explosive tip at the axial end of the detonator and around the circumference of the detonator in the lateral region immediately adjacent the explosive tip. The effective lateral output region of a prior art detonator typically does not exceed a distance along the longitudinal axis of the detonator which is equal to the diameter of one usual-sized receptor line, e.g., shock tube or a low-energy detonating cord. Accordingly, most prior art connector blocks are configured to hold receptor lines only against the explosive tip of the detonator and at opposite sides of the detonator, immediately adjacent the explosive tip.
An exception to such placement of the receptor lines is shown in U.S. Pat. No. 6,349,648, issued to J. Capers et al on Feb. 26, 2002, which is a division of U.S. Pat. No. 6,305,287, issued to J. Capers et al on Oct. 23, 2001. The '648 Patent, like the '287 Patent, discloses a detonator and a connector block for holding the same in contact with a plurality of receptor lines. As best seen in FIGS. 1E, 2, 3 and 5, and as described starting at column 3, line 54, the detonator B is formed from a generally cylindrical metallic shell of circular cross-section, preferably formed from aluminum about 0.5 mm thick and shaped as shown in FIG. 5. Detonator B is comprised of a main cylindrical section 10, a smaller-diameter cylindrical explosive end portion 12, and a transition portion 14. The shell of detonator B is said to preferably be axisymmetric with respect to its longitudinal axis 15 (FIG. 5). The main (output) explosive charge of detonator B is located in explosive end portion 12 (FIGS. 6 and 7), and is distributed along the axial length of end portion 12 so as to initiate shock tubes D (FIG. 1B). The explosive force of the ignited main charge will ignite the shock tubes D held in place alongside the length of end portion 12. An initiating shock tube 16 is connected to the opposite signal end 18 of detonator B, as best seen in FIGS. 1E, 2 and 3.
The connector block, referred to as “block body A”, is described starting at column 4, line 20 and is configured to hold a plurality of shock tubes D orthogonally to explosive end portion 12. As illustrated in FIGS. 6 and 7, and described at column 5, line 61 to column 6, line 62, various loadings of explosives such as PETN and dextrinated lead azide may be loaded within end portion 12. FIG. 6 shows the interposition of a small, fast-burning pyrotechnic charge 64, e.g., a zirconium/red lead mixture, placed on top of the main lead azide charge in order to “protect against explosion of the charges during subsequent loading operations.” (Column 6, lines 13–17.) FIG. 7 shows an embodiment in which the PETN charge is filled to above the transition point between the small-diameter explosive end portion 12 and main cylindrical section 10. These expedients show attempts to deal with the difficulties inherent in loading the explosive and pyrotechnic components into the end of a detonator which transitions from a large diameter to a smaller diameter end portion.